1. Field of the Invention
The invention relates to an assembly and a method for mounting a pump bearing in/on plastic coolant pump housings.
2. The Prior Art
In the prior art, coolant pumps having plastic housings are previously described.
In the case of these designs, the pump bearing is positioned into an injection-molding die before injection molding, and integrated into the plastic housing, in a secure position, during injection molding.
This variant of attaching the bearing has the disadvantages that the pump bearing is exposed to temperatures of up to 300° C. and thereby subjected to very great thermal stress.
During the cooling process, the bearing sleeves are then radially twisted in the plastic, and in this connection are often actually deformed.
In subsequent working steps, the bearings then have to be greased and sealed.
Aside from other increased production and installation effort connected with this, the coolant pumps having injection-molded pump bearings have the additional disadvantage that the bearings used as pump bearings must demonstrate relatively great bearing play, because of the twisting of the outer ring in the plastic, caused by the technology.
This great bearing play necessarily results in a great “unbalance,” which makes it more difficult to provide the shaft seal that must be taken over by the shaft sealing ring, increases the installation effort, reduces the useful lifetime of the bearing, and furthermore causes increased running noises.
Another disadvantage of coolant pumps having a bearing injection-molded into the plastic housing is that these plastic housings cannot be tempered as a result of the integrated pump bearings, because the plastic is heated to 180° C. to 200° C. during tempering, so that the non-tempered plastics necessarily have a lesser strength as compared with tempered plastics.
Furthermore, it is not possible to separate the steel bearings injection-molded in from the plastic of the housing without destroying the housing, so that re-use of the bearing housings is precluded.
Furthermore, recycling of plastic housings having pump bearings injection-molded in is very cost-intensive, since separation of the bearings injection-molded in from the plastic of the housing necessarily requires an increased expenditure of time and/or labor.
On the other hand, bearing assemblies in plastic housings of coolant pumps are previously described, for example in DE 197 20 286 A1, in which the entire mantle surface of the pump bearing is glued into the related plastic housing.
In this connection, production and installation tolerances are predetermined by the adhesive gap between the plastic housing and the outer mantle of the bearing, which is required for transfer of the axial bearing stresses.
However, these production and installation tolerances that are necessarily required for the required adhesive gap significantly influence the sealing gap geometry between the impeller wheel and the related housing bore, and increase the leakage flow as a significant influence variable for the degree of effectiveness of the coolant pump, so that in the case of coolant pumps having pump bearings glued in (at justifiable production and/or installation effort), either only slight bearing stresses can be transferred to the pump housing, or the adhesive gaps are designed in such a manner that great bearing stresses can be transferred to the pump housing. However, these coolant pumps last mentioned then necessarily have a low degree of effectiveness.
In DE 103 00 611 A1, the applicant presented a bearing assembly for pump bearings in/on plastic coolant pump housings, having an axial bearing contact, that has already proven itself, in the meantime, in which a radial housing groove provided with an inlet bore is disposed in the coolant pump housing, on the one hand, and on the other hand, a bearing groove is made on the bearing ring to be disposed in the bearing seat, which groove lies opposite the housing groove in the final assembled state.
Then, for example, polyamide in the liquid state is introduced into the cavity formed between the coolant pump housing and the bearing ring, by the housing groove and the bearing groove, by way of the inlet bore.
After the polyamide has hardened, an injection-molded plastic ring that is connected both with the coolant pump housing and with the bearing ring forms in the cavity between the housing groove and the bearing groove.
However, this construction, which has already proven itself in practice, requires increased production effort for the production of the “adhesive ring,” since the circumferential housing grooves and the bores required for “filling of these housing grooves” have to be mechanically made in the plastic housings subsequently, for the “production” of the adhesive ring.
The radial housing groove to be disposed in the plastic housing of the coolant pump brings about the result that the axle journal is weakened by the placement of this housing groove, so that under extreme belt loads, there is the risk of fracture at this location.
On the other hand, injection of the polyamide, by way of the inlet bore, into the ring-shaped interstice formed by housing groove and bearing groove, requires precise metering of the injection amount and, at the same time, precise monitoring of the filling process, since the polyamide can flow off axially in the direction of the shaft sealing ring, for example, and this can result in impairment of the ability of the radial sealing ring, i.e. the rotating mechanical seal, to function properly, among other things, or can cause incomplete filling of the ring groove, clearly restricting the desired axial and radial securing of the bearing in the plastic housing.
The placement of crosspieces in the bearing bore of the plastic housing, with crosspiece grooves lying between them, which was proposed in connection with the inlet bore and the housing groove in the dependent claims of the aforementioned application, did not result in the desired strength of the adhesive connection in practical implementation, however, since it was not possible to guarantee complete filling of the ring groove and the crosspiece grooves by the viscous adhesive. Therefore, only the solution with an inlet bore that empties into a ring groove was able to establish itself in practice.
As a result of the deficiencies of this solution as described above, it was therefore necessary to develop the mounting of pump bearings in/on plastic coolant pump housings further, in consistent manner.